For centuries, pipeline systems have been used to convey fluid. As early as 4000 B.C., clay pipes assembled into pipeline systems were used for drainage systems which operated on the basis of gravity flow. During Roman times, lead pipes were fabricated and assembled into pipeline systems for drainage. In some instances, tree trunks were bored and used as water or drainage pipes. During the 18th century, lack of sanitation, especially in cities, was considered a major cause of illness. To resolve this problem, pipeline systems were constructed to collect sewage throughout the city for conveyance to a central processing facility. Today, pipeline systems are used for the building, chemical, oil and gas, agricultural and mining industries and for public works applications. These modern pipeline systems convey various types of fluids which can be categorized as gases, liquids, colloidal suspensions and liquid/solid slurries.
In order to monitor and control the flow of the fluid through pipeline systems, in-line process control equipment is installed. In-line process control equipment includes valves, pumps, flow meters, temperature and pressure controllers. In-line equipment usually cannot be welded into the pipeline because time-scheduled maintenance requires temporary removal of this equipment and, occasionally, depleted equipment must be removed for replacement. Typically, in-line process control equipment is installed into the pipeline by joining flanged-end connections of that particular piece of in-line equipment with flanged-end connections of the pipeline. Simply bolting the flanged-end connections of the in-line process control equipment with those of the pipeline is not sufficient to assure adequate sealing between the joined flanged-end connections to prevent leakage. Seal devices are often interposed and compressed between the flanged-end connections so as to prevent leakage of the fluid therebetween.
Before selecting a seal device for a specific application, a myriad of factors is considered. These factors include the corrosive nature of the fluid flowing through the pipeline as well as the physical characteristics of the flowing fluid such as pressure, temperature and velocity. Although numerous types of materials may be considered in fabricating an appropriate seal for a particular application, often, the optimum material is compromised because of other overriding considerations. For example, a highly corrosive gas such as hydrogen sulfide can be conveyed through a pipeline at a high pressure and velocity. Optimally, a polymer material would be desirable for a seal device to prevent the seal device from corroding. However, a polymer material is not desirable under these conditions because of its proclivity to deform under high pressure, thus, compromising the integrity of its sealing capability.
In the past, a conventional tandem seal device has been used for high-pressure applications. This conventional tandem seal device comprises a retainer body having opposite first and second surfaces and a pair of continuous grooves formed into each surface. An O-ring fabricated from elastomeric material is disposed into each of the grooves. Although this conventional tandem seal device is effective for high pressure applications, it is not as effective in a corrosive environment. Again, the integrity of the sealing capability of this tandem seal device is compromised by the selection of a material appropriate for a high pressure environment but inappropriate for a corrosive one.
Another type of seal device which has been used as a standard in the industry for many years is a conventional graphite-filled, spiral-wound seal device. This conventional seal device includes an outer retainer body surrounding an inner seal assembly. The inner seal assembly comprises an outer carbon-steel guide ring which is designed to hold a series of windings of a laminate of a selected metal and a graphite filler. As the metal and graphite filler are wound together within the carbon-steel guide ring, spot weldments are intermittently made to secure the winding within the carbon-steel guide ring. To use this conventional seal device in a corrosive environment, a stainless steel is selected for the metal in the windings. Under nominal pressure conditions, this stainless steel/graphite seal device performs adequately in a corrosive environment.
Yet another fact to consider when selecting material for a seal device is the possibility of fire. For certain applications, local ordinance or fire code may require that the seal device be fire-resistant. Generally, a fire-resistant seal device means a seal device which will expand under extremely high temperature conditions to accommodate the thermal expansion of the joined flanged-end connections during a fire. A fire-resistant seal device is intended to prevent fluid leakage for only a brief period of time so that personnel could be safely evacuated before the flanged-end connection begins to leak.
Although approved under fire code as fire-resistant, the metal/graphite seal device, whether used in a corrosive or non--corrosive environment, is marginally beneficial when exposed to fire. However, in a fire, extreme temperatures can cause the spot weldments of the seal device to melt which, in turn, causes the windings of metal and graphite to burst part. Catastrophic failure of this graphite-filled, spiral-wound seal device results. Further, under high pressure conditions, the conventional graphite-filled, spiral-wound seal device performs only adequately.
Therefore, a need exists in the marketplace to provide a seal device which can perform well under highly corrosive, high temperature and/or high pressure conditions. There is also a need in the industry to provide a fire-resistant seal device which will not readily unwind when subjected to high temperatures generated by fire. It would also be advantageous if a seal could be custom-made for conditions of high pressure and corrosion or conditions of high pressure and fire resistance or conditions of corrosion resistance and fire resistance. The present invention addresses these needs and provides these advantages.